A new, highly selective method is proposed for the analysis of nonvolatile or thermally labile materials. This method brings together four individual techniques: supersonic jet spectroscopy, laser multiphoton ionization, mass spectrometry, and supercritical fluid chromatography. Samples will be dissolved in a supercritical fluid and expanded in a supersonic jet which is interfaced to a mass spectrometer. Isentropic cooling of molecules during the course of the expansion produces sharp ultraviolet-visible absorption bands allowing selective laser ionization of targeted compounds by resonantly enhanced multiphoton ionization. This method should be especially useful in the determination of environmentally important chloro, hydroxyl, and amine derivatives of large aromatic compounds and of biologically important purines, pyrimidines, and alkaloids in complex samples. In addition to analytical applications, the method should provide a new way of investigating the low temperature spectroscopy and dynamics of nonvolatile polar materials. Fundamental aspects of the jet expansion interface will be studied in an effort to optimize performance.